A novel technique to increase the UCN density ... -...
Transcript of A novel technique to increase the UCN density ... -...
A novel technique to increase the UCN
density for J-PARC UCN source
2010/4/9 1UCN2010@RCNP
Tamaki Yoshioka (KEK)
and the NOP collaboration
UCN2010 @ RCNP
International Workshop on UCN
and Fundamental Neutron Physics
J-PARC UCN Source (P33)
Spallation source and
superthermal converter using
sD2 for intense UCN source
CN spectrum
� 6200 UCN/cm3
Proton Beam
J-PARC UCN Source (P33)
Spallation source and
superthermal converter using
sD2 for intense UCN source
CN spectrum
� 6200 UCN/cm3
Novel transportation system
for preserving the UCN
density; called “rebuncher”
Proton Beam
Rebunching process in the
space-time coordinates
J-PARC UCN Source (P33)
Spallation source and
superthermal converter using
sD2 for intense UCN source
CN spectrum
� 6200 UCN/cm3
Novel transportation system
for preserving the UCN
density; called “rebuncher”
Proton Beam
Rebunching process in the
space-time coordinates
nEDM measurement cell.
Downsizing the volume for
reducing systematic error
Deuterated Polystyren
Decay time = 1.3 msDecay time = 1.3 ms
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Production of UCN by a Pulse
Time structure of neutron flux
in D2 converter.
Time structure of neutron flux
in D2 converter.
By rebunching technique,
ρUCN achieves 3100 UCN/cm3/pulse (polarized).
Production time is only 1.3ms.
Maximum UCN density = P × τ
Storage time τ is 140 ms in D2 for T < 4K
100 times of multiplication is possible!!
UCN Juggler
Production time is only 1.3ms.
Maximum UCN density = P × τ
Storage time τ is 140 ms in D2 for T < 4K
100 times of multiplication is possible!!
UCN Juggler
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00 t0t0Converter
Time 0 t0
ττ
τ
Production Rate is fixed as 1 for simplicity.
Beam
Production and loss rate
is at equilibrium condition.
UCN density
UCN Production and StorageDC Beam
UCN Production and Storage
00 t0/2t0/2Converter
Time 0 t0
ττ
2τ
Beam
0 t0/2 τ
Converter to Cell, and
Cell to Converter is
at equilibrium.
UCN density
DC Beam with storage cell
Cell
UCN Production and Storage
00 ∆t ∆t Converter
Time 0 t0
Beam
UCN density never achieve to τ
∆t
For D2 converter
τ~ 146 ms
t0~ 40 ms to 500ms
∆t~ 0.5 ms
2t0
∆t
∆t exp(-t0/τ)
+∆t
∆t exp(-t0/τ)
+∆t
UCN density
Pulse Beam
UCN Production and Storage
Time 0 t0
Beam
Finally UCN density achieve to P×τ !!
∆t
2t0
∆t
UCN density
00Converter
0
∆t∆t
0
∆t∆t
0
Loss in the converter is critical.
UCN have to out of the converter until next pulse.
00
∆t
2∆t2∆t
0
Escape from
converter
Return to
converter
Pulse Beam with cell
Cell
UCN Production and Storage
Time 0 t0
Beam
Finally UCN density achieve to P×τ !!
∆t
2t0
∆t
UCN density
00Converter
0
∆t∆t
0
∆t∆t
0
Loss in the converter is critical.
UCN have to out of the converter until next pulse.
00
∆t
2∆t2∆t
0
Escape from
converter
Return to
converter
Pulse Beam with cell
Cell
UCN Juggler
Possible Scheme of the UCN Juggler
1) Rebuncher focus UCN on mirror.
2) Reflected UCN focused on converter
again.
3) Proton pulse synchronizes the
returned UCN. Then phase space of
incoming and produced UCN
overlaps.
4) Repeat 1)~3)
5) Open the top mirror.
1) Rebuncher focus UCN on mirror.
2) Reflected UCN focused on converter
again.
3) Proton pulse synchronizes the
returned UCN. Then phase space of
incoming and produced UCN
overlaps.
4) Repeat 1)~3)
5) Open the top mirror.
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Some Concerns
• Spin exchange is critical; incoherent scattering of D2,
depolarization etc. (Spinless nuclei, 4He, 16O, or 208Pb can
be the candidates)
• Elastic scattering might be problem; Converter must be
thinner.
• Loss of rebuncher must be less than 1%.
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Ideal Maximum UCN Density (for sD2)
• By 400MeV-50mA-0.5ms (10kW) pulse,
ρUCN = 6200 UCN/cm3/pulse.
• Moderation time of cold neutron is 1.3 ms (FWHM).
• If UCN Juggler is ideally working, UCN density can
achieve
ρUCN = 6200 UCN/cm3 × (146ms/1.3ms) × 1/2
= 3.5 × 105 UCN/cm3
• Note : Temperature increase is 0.15K for a pulse.
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Summary• UCN density in moderator is calculated to be
6200 UCN/cm3/pulse. Rebuncher can transport 3100
UCN/cm3/pulse.
• We propose new technique to increase the UCN
density
to utilize the pulse beam of J-PARC. � UCN juggler
• UCN juggler can multiply the UCN density of on pulse
by 100 times.
• R&D studies will be performed by using the UCNs
produced by newly constructed Doppler Shifter (Next
Talk).